1. Field of the Invention
This invention relates in general to method and apparatus for making color corrections during the manufacture of printing forms.
2. Description of the Prior Art
Correction circuits for the manufacture of printing forms exist, for example, using color computers in color scanners and color converters in color display instruments like color previewer. A color scanner serves the purpose to produce color corrected color separations for the multi-color printing industry. So as to generate the color value signals, a color original to be reproduced is scanned by an optical electronic device. A color computer converts the color value signals according to the laws of substractive color mixing into the proper color separation signals which are amplified and fed to an recorder system. These recorder systems expose film and the exposure intensity is regulated by the modulations of the color separation signals. These films become after development the corrected color separations Magenta, Cyan and Yellow for the multi-color printing operations.
The color correction takes into account the errors of the reproduction process and make it possible to change the reproduction with respect to the original according to the desired color effect required by the customer.
The color computer calculates from the color value signals correction signals and superimposes these signals onto the color value signals so that the actuation of these color signals must be done manually in all known color computers by means of control units. Since a wide range of corrections are required and offered any color computer in the form of the base selective or part image correction, a multitude of correction parameters must be registered, fixed and at a later time as required for the actual reproduction process be then transferred to one or several color computers.
The correction parameters of a color computer can be obtained either in the color scanner itself or with the aid of a color previewer. For this purpose the color computer is removed during the determination of these parameters from the color scanner and switched into the input circuits of the color previewer.
A color previewer simulates the printing results with the aid of a TV screen of a color monitor. This makes it possible to simultaneously visually judge the effect of a correction while the color computer is adjusted and makes it possible to check the final results on the TV screen. The color previewer generates by scanning an original image which is to be produced with the help of a color television camera three color value signals which correspond to the output signal of an optical electronic scanner in a color scanner. These color value signals are transformed in the color computer which has to be adjusted into the corrected color separation signals.
A color transformer follows the color computer stage which transforms the color separation signals into the input signals for the color monitor so that the representation on a TV screen will be of the same appearance as the finished multi-color print.
So that this multi-color print simulation will be true in color a large number of correction parameters must be used for the correction of a color transformer and these are set by manually activated controls. A new program for the color transformer is for example always required when a particular custom or job changes or when the printing process changes or the printing ink or the printing paper for the following printing processes are changed. Thus, there are many disadvantages of prior art correction circuits. Also, during a test run, a multitude of correction parameters must first be adjusted by manually changing the control settings of an input system and by measuring and observing the corrections. Once the proper correction parameters are established they have in the prior art been written down in form of a table such that they can be used at a later time and/or whenever the need arises they can again be transferred manually into one or several correction circuits.
Such operations are time consuming and expensive and they do not allow for standardization or automation of the reproduction processes. Additionally, the accuracy in the determination of the correction parameters in their reproducibility when transferred to a correction circuit depends to a large extent on the dexterity and color perception of a particular operation. Additionally, it is important for an economical reproduction process that the time required for the adjustment of the correction circuits be comparatively short relative to the time required for recording of the color separation values. Short set up times are only possible however, if many adjustments are simplified and can be accomplished automatically.